The production of solid materials based on polysaccharides, which may also comprise additives, with the aid of chaotropic liquids, especially ionic liquids, is known from the international and US patent applications and the US patents WO 03/029329 A2, US 2003/0157351 A1, WO 2004/084627 A2, US 2004/0038031 A1, U.S. Pat. No. 6,824,599, U.S. Pat. No. 6,808,557, US 2004/0006774 A1, WO 2007/057235 A2 and WO 2007/085624 A1.
In these known processes, a polysaccharide, especially cellulose, is dissolved in an ionic liquid, optionally together with additives. Subsequently, the solution is introduced into a liquid medium which is miscible with the ionic liquid but which is incapable of dissolving the polysaccharide. This regenerates the polysaccharide. Suitable liquid media comprise water, alcohols, nitriles, ethers or ketones, or consist thereof. Preference is given to using water because it is then possible to dispense with the use of volatile organic solvents. Typically, the regenerated polysaccharide is obtained in the form of a gel. In the course of drying, however, the regenerated polysaccharide gel shrinks very significantly, which is a serious disadvantage especially in the case of production of films.
These disadvantages, however, occur not only in the case of production of films, but also in the case of production of regenerated polysaccharide in other three-dimensional forms. For instance, these disadvantages complicate the controlled and reproducible production of powder particles based on regenerated polysaccharide, such that the powder particles are not an option for numerous applications for technical and economic reasons.
International patent application WO 2004/083286 A1 discloses a process for producing films from cellulose and the water-soluble polysaccharide xylan. The films are produced only using water. The films may comprise plasticizers such as water, sugar, ethylene glycol, propylene glycol, butanediol, glycerol or urea. The international patent application does not give any suggestions or hints as to how the disadvantages of the known processes in which ionic liquids are used could be avoided.
American patent application US 2006/0151170 A1 discloses a process for stimulating mineral oil and natural gas sources. In this process, a thickened liquid medium which comprises deformable particles in the form of pellets, cylinders, cubes, rods, cones or irregular forms of particle diameter 850 μm is injected into a borehole under pressure. This forms new cracks and fissures in the mineral oil or natural gas formation, through which the mineral oil or natural gas again has easier access to the borehole. This process for borehole stimulation is also referred to as “fracturing” in the natural gas and mineral oil extraction industry. The deformable particles serve as support particles or support materials which prevent the newly formed cracks and fissures from closing again as a result of the pressure of the rock above. These support particles or support materials are also referred to as “proppants” in the natural gas and mineral oil extraction industry. The deformability of the proppants prevents, to a certain degree, the formation of fine material as a result of abrasion of rock material, and/or as a result of crushing of the proppants, as frequently occurs in the case of use of hard proppants, such as fracturing sand. The deformable proppants thus effectively have the effect of support cushions.
In the known fracturing process, deformable proppants composed of comminuted natural substances are used, for example chipped, ground or crushed nutshells, fruit seeds, plant husks or wood parts. However, these have to be provided with a protective layer in order to adjust the modulus of elasticity of the proppants to the particular requirements. Furthermore, the known deformable proppants have the disadvantage that the chemical compositions thereof and the mechanical properties thereof vary significantly, such that complex tests are required to check whether a supplied batch is suitable for a given mineral oil or natural gas formation.